This invention relates to a method for manufacturing a gas sensor having a tubular housing and a sensing element disposed in this housing.
For example, an oxygen sensor or a comparable gas sensor is equipped in an internal combustion engine to measure an oxygen concentration. This sensor comprises a tubular housing and a sensing element disposed in the housing. The housing has an inner cylindrical stepped portion protruding radially inward from an inner cylindrical surface thereof. The sensing element has a flange portion protruding radially outward from an outer surface thereof. The flange portion of the sensing element is placed on the inner cylindrical stepped portion of the housing. Talc powder or other inorganic powder is stuffed into a contact portion between the sensing element and the housing.
In stuffing such inorganic powder into the contact portion, a hardened powder ring is inserted into an annular end space defined between the inner cylindrical surface of the housing and the outer surface of the sensing element. The hardened powder ring is a hardened block of inorganic powder configured into a ring shape. The hardened powder ring is pressed and crushed.
However, according to the above-described conventional gas sensor manufacturing method, it is difficult to uniformly apply a pressing force to the hardened powder ring or the inorganic powder stuffed into the annular end space. This leads to nonuniform density distribution of the inorganic powder in the annular end space. Airtightness will be worsened.
Furthermore, in the pressing operation of the hardened powder ring, the pushing member may accidentally hit or collide with the sensing element or the housing and accordingly may damage the sensing element or the housing. If the sensing element is damaged, the output characteristics of the gas sensor will possibly deteriorate. If the housing is damaged, a small or sliced piece of housing material may mix into the inorganic powder. This will cause insulation defectiveness or other problem.
In view of the foregoing problems of the prior art, the present invention has an object to provide a manufacturing method for a gas sensor according to which no damage is given to the sensing element or the housing and the inorganic powder can be uniformly stuffed into the annular end space between the sensing element and the housing.
To accomplish the above and other related objects, the present invention provides a first method for manufacturing a gas sensor having a tubular housing and a sensing element disposed in the housing. The first manufacturing method of this invention comprises a step of inserting the sensing element into the tubular housing from a rear end toward a front end of the housing. The sensing element has a flange portion protruding radially outward from an outer surface thereof, and the housing has an inner cylindrical stepped portion protruding radially inward from an inner cylindrical surface thereof. The first manufacturing method of this invention further comprises a step of placing the flange portion of the sensing element on the inner cylindrical stepped portion of the housing, and a step of inserting a hardened powder ring into an annular end space defined between the inner cylindrical surface of the housing and the outer surface of the sensing element. The hardened powder ring is a hardened block of inorganic powder configured into a ring shape. The first manufacturing method of this invention further comprises a step of pressing the hardened powder ring toward the front end of the housing by a tubular pushing member and crushing the hardened powder ring into inorganic powder by the tubular pushing member so that the annular end space is stuffed by the inorganic powder. According to the first manufacturing method of this invention, the following relationship is satisfied
0.275 mmxe2x89xa6rpxe2x88x92Rexe2x89xa60.375 mm,
and
0.15 mmxe2x89xa6rhxe2x88x92Rpxe2x89xa60.25 mm,
where rp represents an inner radius of the pushing member, Rp represents an outer radius of the pushing member, rh represents an inner radius of the housing, and Re represents an outer radius of the sensing element at a portion substantially defining the annular end space.
This invention has the following functions and effects.
According to this invention, the inner radius rp and the outer radius Rp of the pushing member satisfy the relationship 0.275 mmxe2x89xa6rpxe2x88x92Re and 0.15 mmxe2x89xa6rhxe2x88x92Rp with respect to the outer radius Re of the sensing element and the inner radius rh of the housing. With this arrangement, it becomes possible to secure a sufficient clearance necessary for smoothing the insertion of the pushing member which is inserted into the annular end space. Namely, it becomes possible to secure a sufficient clearance between the pushing member and the housing and also secure a sufficient clearance between the pushing member and the sensing element.
Furthermore, the inner radius rp and the outer radius Rp of the pushing member satisfy the relationship rpxe2x88x92Rexe2x89xa60.375 mm and rhxe2x88x92Rpxe2x89xa60.25 mm with respect to the outer radius Re of the sensing element and the inner radius rh of the housing. With this arrangement, it becomes possible to sufficiently reduce or narrow the clearance between the pushing member and the housing as well as the clearance between the pushing member and the sensing element, when the pushing member is inserted into the annular end space. Accordingly, it becomes possible to uniformly press the hardened powder ring or the inorganic powder in the entire region of the annular end space.
As described above, this invention provides a method for manufacturing a gas sensor capable of uniformly stuffing the inorganic powder into the annular end space defined between the sensing element and the housing without damaging the sensing element and the housing.
According to the above-described first manufacturing method of the present invention, it is preferable that the pushing member has a press portion consisting of a flat surface, an inner curved surface having a curvature radius of 0.3xcx9c0.4 mm, and an outer curved surface having a curvature radius of 0.3xcx9c0.5 mm. The inner curved surface is formed at a radially inner end of the press portion. The outer curved surface is formed at a radially outer end of the press portion.
When the press portion of the pushing member has inner and outer curved surfaces having the above-described curvature radiuses, the press portion of the pushing member does not hit or collide against the outer surface of the sensing element as well as against the inner surface of the housing. No damage is given to the sensing element and the housing.
As described above, the inner radius rp and the outer radius Rp of the pushing member satisfy the above-described conditions. The press portion of the pushing member has the inner and outer curved surfaces having the above-described curvature radiuses. Thus, it becomes possible to uniformly stuff the inorganic powder into the annular end space without damaging the sensing element and the housing.
The present invention provides a second method for manufacturing a gas sensor having a tubular housing and a sensing element disposed in the housing, comprising:
a step of inserting the sensing element into the tubular housing from a rear end toward a front end of the housing, the sensing element having a flange portion protruding radially outward from an outer surface thereof, and the housing having an inner cylindrical stepped portion protruding radially inward from an inner cylindrical surface thereof;
a step of placing the flange portion of the sensing element on the inner cylindrical stepped portion of the housing;
a step of inserting a hardened powder ring into an annular end space defined between the inner cylindrical surface of the housing and the outer surface of the sensing element, the hardened powder ring being a hardened block of talc powder configured into a ring shape;
a step of inserting a packing ring in the annular end space to dispose the packing ring on the hardened powder ring, the packing ring being made of an inorganic member different from the hardened powder ring,
a step of inserting a guide into a rear end of the sensing element, the guide being disposed inside an annular pushing member and slidable in an axial direction of the pushing member,
a step of sliding the pushing member along the guide toward the front end of the housing, thereby pressing the hardened powder ring via the packing ring by the pushing member and crushing the hardened powder ring into talc powder by the tubular pushing member so that the annular end space is stuffed by the talc powder;
wherein the following relationship is satisfied
0.275 mmxe2x89xa6rpxe2x88x92Rexe2x89xa60.375 mm,
and
0.15 mmxe2x89xa6rhxe2x88x92Rpxe2x89xa60.25 mm,
where rp represents an inner radius of the pushing member, Rp represents an outer radius of the pushing member, rh represents an inner radius of the housing, and Re represents an outer radius of the sensing element at a portion substantially defining the annular end space, and
the pushing member has a press portion consisting of a flat surface, an inner curved surface having a curvature radius of 0.3xcx9c0.4 mm, and an outer curved surface having a curvature radius of 0.3xcx9c0.5 mm, the inner curved surface being formed at a radially inner end of the press portion while the outer curved surface being formed at a radially outer end of the press portion.
According to the second manufacturing method of the present invention, it becomes possible to surely manufacture a gas sensor capable of uniformly stuffing the inorganic powder into the annular end space defined between the sensing element and the housing without damaging the sensing element and the housing.